1. Field of the Invention
The present invention relates to an optical printing head of a side-printing device for printing data on a side margin of a photosensitive material, like a photo filmstrip. More particularly, the present invention relates to an optical printing head having a plurality of light emitting elements which are arranged side by side and so partitioned that light beams from the individual light emitting elements will not be mixed.
2. Background Art
Manufacturing processes of photosensitive materials include a side-printing process for photographically printing film data in the form of characters, marks and bar codes on a side margin of the photosensitive material outside those areas used for photographing picture frames. The film data printed on the side margins includes a manufacturer""s name, and ISO sensitivity or film speed of the photosensitive material. The film data is side-printed as a latent image and is developed as visible images concurrently with the picture frames photographed on the photosensitive material. Thereafter, the film data is manually or mechanically read out and utilized as film data for controlling printing the photographed images.
The side printing process uses a specific optical printing head, hereinafter called the side-printing head. An example of the side-printing head is disclosed in Japanese Laid-open Patent Application No. 2-100043. The side-printing head of this prior art has a light source consisting of an array of light emitting diodes (LEDs), each LED consists of LED chips emitting rays of different wavelengths. An inlet end of a large diameter optical fiber is placed in opposition to each LED. An outlet end of the large diameter optical fiber is connected to an optical fiber bundle that consists of a plurality of small diameter optical fibers, so the rays from the light source is projected from outlet ends of the small diameter optical fibers.
The rays of different wavelengths are mixed uniformly with each other through the large diameter optical fiber, and then an uniformly mixed light beam is projected from the outlet end of each individual optical fiber bundle. The outlet ends of the optical fiber bundles are arranged in a line perpendicularly to a conveying direction of the photosensitive material. Some of the LEDs are sequentially turned on and off in synchronism with the conveying movement, and the light beams from the outlet ends of the optical fiber bundles are projected through a converging lens system onto the side margins of the photosensitive material, printing latent images of characters, marks or bar codes.
Another example of a side-printing head is disclosed in Japanese Laid-open Patent Application No. 58-219543, wherein an array of LEDs are aligned in a perpendicular direction to a conveying direction of a photosensitive material, to project light beams toward the photosensitive material. Each of the LEDs corresponds to one pixel of one line of a latent image, and is connected to an LED driver. In synchronism with the conveying movement of the photosensitive material, the LEDs are turned on or off in accordance with their positions in the array. Light beams from the LEDs are focused through a converging lens system onto a side margin of the photosensitive material, thereby recording latent images of characters, marks and bar codes.
The former prior art has a problem in that the amount of light at the outlet end of the optical fiber bundle is remarkably lessened from the light amount from the LED. In addition, the apparatus is complicated in structure and expensive, and needs a large installation space. On the other hand, the latter prior art has a problem in that the light beams from the neighboring LEDs can interfere with each other. In that case, the individual pixels cannot be recorded at proper densities or in proper dot patterns. It is possible to prevent the interference between the light beams by providing enough spacing between the LEDs. However, the wider the spacing between the LEDs, the spacing between the pixels of the printed image becomes the wider, lowering the quality of the printed image.
In view of the foregoing, an object of the present invention is to provide an optical printing head of a side-printing device, that prevents interference between those light beams which are to be used for printing different pixels, provides good quality of printed images, and is compact and inexpensive.
Another object of the present invention is to provide a side-printing device using such a side-printing head.
According to the present invention, an optical printing head of a side-printing device for printing data of a photosensitive material as a latent image on a side margin of the photosensitive material while the photosensitive material is being conveyed in a direction the optical printing head comprises a plurality of light emitting elements mounted on a substrate and arranged along a perpendicular direction to the conveying direction of the photosensitive material; a partitioning device mounted on the substrate, for partitioning the light emitting elements from each other, to prevent interference between rays from adjacent ones of the light emitting elements; a diffusion device for diffusing rays from the light emitting elements, to equalize luminance of rays from each light emitting element; and a converging lens system for projecting rays from the light emitting elements onto the photosensitive material, wherein each of the light emitting elements is assigned to record a dot at a time when driven in synchronism with the conveying movement of the photosensitive material, thereby to print the latent image line by line.
Since the optical printing head of the present invention does not use any optical fibers, luminance reduction is remarkably suppressed in comparison with the above described prior arts, so the optical printing head of the present invention is useful for the side-printing on a low speed photosensitive material, or achieves a high speed side-printing process, or may use a lower current for driving the light emitting elements. Omitting the optical fibers also simplifies the structure, cuts the cost of the printing head, and makes the printing head compact and sturdy.
According to a preferred embodiment, the optical printing head further comprises a mask plate disposed between the diffusion device and the converging lens system, the mask plate having openings in correspondence with the light emitting elements, the openings having a shape equal to an expected shape of the dot.
According to another aspect of the present invention, a side-printing device for printing data of a photosensitive material as a latent image on a side margin of the photosensitive material while the photosensitive material is being conveyed in a direction, comprises three optical printing heads for emitting rays of three colors respectively, and each of the optical printing heads comprises a plurality of light emitting elements mounted on a substrate and arranged along a perpendicular direction to the conveying direction of the photosensitive material, the light emitting elements emitting rays of one of the three colors; a partitioning device mounted on the substrate, for partitioning the light emitting elements from each other; a diffusion device for diffusing rays from the light emitting elements; and a converging lens system for projecting rays from the light emitting elements onto the photosensitive material, wherein each of the light emitting elements of the three optical printing heads is assigned to record a dot of one color at a time when driven in synchronism with the conveying movement of the photo sensitive material, thereby to print the latent image line by line in the three colors.